Walchem’s solenoid valves open when the coil is energized, and close when de-energized. When the coil is energized, the pilot valve opens, relieving the pressure above the piston, which is lifted from its seat by the laminar plunger. When de-energized, a spring closes the pilot valve and opens a bleed passageway to permit pressure to build above the piston and seat it. No differential pressure is required to open the valve.
